Ensure that we set a text/plain mimetype when a server delivers data with no mime_type and requested no sniffing.

Bug: 932767
Change-Id: I83a1af0cd2ac1626492624dbfd6b6010fc70ca0a
Reviewed-on: https://chromium-review.googlesource.com/c/1476176
Reviewed-by: Clark DuVall <cduvall@chromium.org>
Commit-Queue: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632880}
3 files changed